Recently, various functional materials have been developed. Such functional materials are prepared according to their intended use and used in certain environments. However, when materials are used in certain environments for a long period of time, the surface of many of the materials may be physically or chemically damaged, and thus may lose its original function. In the most general cases, the surface of materials may lose its characteristics due to atmospheric water or fine particles, organisms or the like. For this reason, these days, many researchers are attempting to protect materials from external environments. The most general attempt to solve the above-described problems is to impart superhydrophobicity to the surface.
Materials having superhydrophobic surface have low surface energy, and thus can effectively prevent other materials including water from aggregating on the surface and prevent the adhesion of organic matter, such as human fingerprints, and foreign matter such as dust, to the surface. Thus, materials having superhydrophobic surface can be widely applied to exterior materials for electronic products, in which contamination with organic matter is problematic, or to building materials that need to be protected from moisture or foreign matter. For these reasons, these days, many scientists are attempting to render superhydrophobicity to the surface of materials.
Conventional methods used to impart superhydrophobicity to the surface of materials, particularly stainless steel, typically include a method of coating the surface with titanium or a fluorine-based hydrophobic material such as Teflon. Among these methods, the method of forming titanium or titanium oxide on the surface has a problem in that the resulting surface has a water contact angle of less than 150°, suggesting that it has low hydrophobicity. Another problem is that a high-vacuum deposition process is used, which is performed at high temperatures and it can damage the material onto which coating is performed. Moreover, it increases the production cost. In addition, in the method of coating the surface with a fluorine-based hydrophobic material such as Teflon, the resulting surface has high hydrophobicity, but the vacuum deposition process is also used, which greatly increases the production cost when it is applied to a large-area surface. In an attempt to solve this problem, methods of coating the surface of materials with the fluorine-based hydrophobic material, and the like, have been studied, but there still remains a problem in that the fluorine-based hydrophobic material itself is expensive, which increases the production cost. Thus, there is an urgent need to develop technology of imparting superhydrophobicity to a large-area surface at low costs.
In addition to this, engineering the surface properties of a porous material to have both superhydrophobicity and hydrophilicity is of extreme difficulty. In case of porous materials, imparting superhydrophobicity on one surface will also convert the opposite surface owing to the porousity of the material.
Recently, various methods of preparing Janus microparticles having a hydrophilic surface and a hydrophobic surface have been developed. For instance, Janus particles have been fabricated using photopolymerizable droplets (Kim et al., AngewandteChemie International Edition. 49(14), 2535-2538, 2010). This method comprises treating photopolymerizable resin in an aqueous dispersion of a surfactant by a microfluidic device to prepare droplets having a uniform size and photopolymerizing the droplets to prepare spherical polymeric microparticles. Particularly, in this method, a hydrophilic surface and a hydrophobic surface can be formed on the two hemispheres of the microparticles by removing particles from the interface of the spherical microparticles and exposing the spherical microparticles to SF6 plasma. These Janus microparticles can form a superhydrophobic barrier on the water surface at the water-air interface in the direction of the hemispheres depending on the surface characteristics of the Janus microparticles.
However, these methods focus on fabrication of Janus materials and not converting an arbitrary material to have Janus property. Also, this method has a shortcoming in that a process of orienting the two hemispheres in a desired direction is required in order to impart superhydrophobicity to such Janus microparticles having two surface characteristics.
Accordingly, the present inventors have made extensive efforts to solve the above-described problems, and as a result, have found that a material having a superhydrophobic region and a hydrophilic region can be prepared by preparing a superhydrophobic surface body using initiated chemical vapor deposition (iCVD) and hydrolyzing one surface of the superhydrophobic surface body using a strong base, thereby completing the present invention.